With the development of network technologies, the wireless communication technology has been widely used in people's daily life. To satisfy users' various demands for data transmission in different usage environments, various communication transmission technologies and standards have been developed correspondingly. The 3rd Generation Partnership Project Evolved Universal Terrestrial Radio Access (3GPP E-UTRA) standard is just one of the communication systems that become very popular in recent years.
The handoff mechanism in the current 3GPP E-UTRA standard evaluates a present reference signal received quality (RSRQ) of a user equipment (UE) every fixed period of time, uses a fixed reference signal received quality as a threshold for triggering a handoff, and compares a signal strength received quality with the threshold to determine whether to perform execute the handoff process. In detail, the base station transmits a measurement control message (MCM) periodically based on a fixed period to the UE, and requests the UE to monitor a present reference signal received quality and transmit a measurement report message (MRM) to the base station according to the monitored reference signal received quality. When the present reference signal received quality is lower than the threshold for triggering the handoff, the handoff process is activated.
However, because a fixed reference signal received quality is used as a threshold for triggering the handoff and serves as a basis for the handoff decision in the 3GPP E-UTRA standard, a Ping-Pong effect or a situation in which a handoff is initiated too late (hereinafter referred to as a too-late handoff) is likely to occur. The Ping-Pong effect refers to a phenomenon of repeatedly performing the handoff process back and forth between two base stations when the UE approaches the edge of the two base stations' coverage. Moreover, when the UE moves at a relatively high speed, the reference signal received quality will degrade too rapidly in the handoff process due to the excessively large variance of the reference signal received quality. Consequently, the connection might be disconnected to cause failure of the handoff process.
Accordingly, an urgent need exists in the art to provide a handoff mechanism adapted to trigger the handoff process timely so as to avoid the Ping-Pong effect or a too-late handoff.